We plan to carry on different studies concerning the regulation of the IgE immune response: 1. Ontogeny of IgE synthetizing cells. We want to study the time of apparition of the immunoglobulin receptors on the cell membranes and consider the physiological role of these receptors. 2. Genetic control of the IgE immune response. We are developing a system of 5 congenic lines between two inbred strains of rats which are respectively high and low responders for IgE antibody production to ovalbumin stimulation. This system may allow the analysis of the role of the Kappa chaim repertoire (Kappa chain represents 95% of the heavy chain molecule in the rat species), that of the heavy chain repertoire, that of both the Kappa and heavy chains together, and that of the Rt-1 locus (major histocompatibility locus) alone and in association with the immunoglobulin synthesis loci of the low responder strain in the high responder background. We hope to have the complete model soon but we can start the investigation with the already ready strains. 3. Regulation of the IgE immune response: We plan to investigate into these regulating mechanisms by studying the enhancement of the reaginic response after irradiation using our congenic model and transfer of specialized populations.